In the production of for example cigarettes first filter rods comprising so-called filter tow strips are generated. The filter tow strips can comprise for example cellulose acetate or polypropylene filaments. The filter tow strips are pulled from a pack or stack and further processed on a filter rod machine to form filter strands around which is wrapped paper whereupon, lastly, individual filter rods are generated by cutting the filter strands. The filter rods are cylindrical units around which is wrapped paper having a length of approximately 66 to 150 mm and a diameter of for example 4 mm to 10 mm. Each filter rod normally comprises enough material for four or six filter pieces or filter plugs which are later fastened on tobacco strands by means of a cigarette making machine in order to manufacture filter cigarettes.
In the production of filter strands or filter rods by the filter strand producing machine as well as also in the production of the filter cigarettes proper by means of cigarette machines, rejects or discards are always produced during the operation of these machines. These discards or "waste" comprise valuable substances or materials, such as for example the filter material in the form of cellulose acetate, tobacco and wrapping paper for the tobacco. In order to be able to reutilize in particular the valuable cellulose acetate, the paper which is wrapped around the filter material must be removed from it.
In U.S. Pat. No. 4,457,317 is described a method for removing wrapping paper from cigarette filter rods in which the waste material or the rejected material of the cigarette filter rod is heated to the melting point of the thermoplastic adhesive agent which holds together the paper wrapping. Thereupon the paper wrappings are separated from the filter pieces or filter rods. Subsequently a stream of heated gas is directed around the waste material whereupon the adhesive agent under the influence of the heat liquifies and the paper wrapping becomes detached from the cellulose acetate fiber material. Through the different weights or through the different forms of the cellulose acetate material and the paper wrapped around it, the separation and sorting of these two components can be carried out in the air stream since the paper is transported by the air stream further upward than the heavier filter material.
In the separating and sorting process known from U.S. Pat. No. 4,457,317 difficulties are encountered with respect to a clean sorting of the filter and of the paper material since the temperature profile of the air or gas stream is not constant and therefore between paper and the filter material adhesions always occur. Moreover, the sorting by way of gas stream is expensive since it is also a function of the flow properties of the materials to be separated. If the separation properties of paper and filter material are very close the separation by means of the gas stream is difficult to carry out.
From the cigarette industry is known that in the production of cigarettes waste accumulates. The discarded cigarettes are therefore for example cut open at the cigarette wrapping paper and the tobacco is mechanically removed from the cigarette sleeve. This measure permits the recovery of the valuable tobacco but not the recovery of the valuable filter material of for example cellulose acetate.